I'm running Debian Testing (kernel 5.10.0-2-amd64 / systemd 247.2-5) on a Mac Pro as a NAS / VM host. Today, I added a Thunderbolt 3 card (Gigabyte Titan Ridge) - and noticed something strange: the network identifiers of the Mac's built-in Ethernet ports (enp9s0 / enp10s0) change to enp14s0/enp15s0 depending on whether my iMac is attached and powered on via Thunderbolt at boot time.
What is causing this? I thought the advantage of the "new" naming scheme over good old "ethX" was that the device names are predictable. It is especially annoying as I have to hard-code the interface name in the GRUB commandline so that pre-boot DHCP works so that I can unlock the encrypted root disk, and I also need stable interface names for the bridge configuration.
(Additionally: neither boltctl nor tbtadm recognize the card or connected devices, but the kernel does, and network connectivity works just fine. Why?)